The identification of genes contributing to the etiology of Parkinson's disease (PD) is very complicated. The disorder, in all likelihood, is not a disease with a single cause. A growing body of evidence indicates that PD might be caused by genetic defects and/or by as yet undefined environmental insults acting on genetically predisposed individuals in the process of aging (Langston, 1998; Goldman et al., 1998).
Genetic factors have been linked to familial PD (fPD) or parkinsonism by the demonstration of mutations in the α-synuclein gene (Polymeropoulos et al., 1997), in the parkin gene (Kitada et al., 1998), in the tau gene (Clark et al., 1998), and in several undefined genes mapped to 1p35 (Valente et al, 2001), 1p36 (Van Duijn et al, 2001), 2p13 (Gasser et al., 1998), 4p15.7 (Farrer et al., 1998), and 4p14 (Leroy et al., 1998) and 12p11.2–q13.1 (Funayama et al., 2002). Defective or decreased expression of genes that regulate the development and survival of midbrain dopaminergic (DAergic) neurons may be an important risk factor associated with PD.
The evidence for genetic factors in sporadic PD (sPD) was initially quite controversial (Langston, 1998), but there is now increasing evidence suggesting a significant role for genetic factors in determining PD susceptibility. Recent studies using sensitive PET imaging to detect subclinical nigral dysfunction have shown a higher concordance among monozygotic than dizygotic twins (Piccini et al., 1999). In addition, the combination of a certain α-synuclein promoter polymorphism within the APE4 allele has been suggested to elevate the risk of sporadic PD (Kruger et al., 1999). The data, taken together, suggest strongly that genetic susceptibility factors contribute, either directly or indirectly, to the onset of PD.
NURR1 is highly expressed in the midbrain DAergic neurons (Saucedo-Cardenas et al., 1997). Furthermore, NURR1 is essential for the development of DAergic neurons in the midbrain. Depletion of Nurr1 results in a selective agenesis of mesencephalic DAergic neurons (Zetterstrom et al., 1997; Castillo et al., 1997; Saucedo-Cardenas et al., 1998, Le et al., 1999). Nurr1 is also a transcriptional activator of endogenous tyrosine hydroxylase, a key DA synthesis enzyme (Sakurada et al, Development, 1999), and an enhancer of DA transporter transcription (Sacchetti et al, J Neurochem, 2001).
NURR1 is critical for the survival of late DAergic precursor neurons (Saucedo-Cardenas et al., 1998, Wallen et al., 1998). In the absence of NURR1 during the late stage of development in the NURR1 null mutant mice, the midbrain DA precursor cells degenerate and die of apoptosis. Furthermore, acutely reduced expression of NURR1 (e.g., by antisense knockdown) impairs the expression of the DAergic phenotype in adult SN (Apostolakjs et al., 2002). Reduction of NURR1 expression (e.g. in NURR1+/− mice) confers increased susceptibility to MPTP-induced nigral injury (Le et al., 1999), and decreased DA transmission in the nigral-striatal pathway (Zetterstrom et al., 1997).
The human NURR1 (SEQ ID NO: 1) (also known as NOT/TINUR/RNR-1/HZF-3, a homolog of rodent Nurr1) has been mapped on chromosome 2q22-23 (Mages et al., 1994, and is approximately 8.3 kb long and consists of eight exons and seven introns (Ichinose et al., 1999). The NURR1 gene is highly conserved, and the expression of the gene is mediated by various transcriptional factors and binding sites in the promoter region (Castillo et al., 1997). Wild type NURR1 expressed as a protein having the amino acid sequence of SEQ ID NO: 2.
In addition, NURR1 may have at least two splicing variants in the human brain (Ichinose et al., 1999). Different deletion mutants were constructed in the promoter region of NURR1 and in the transcriptional initiation sites. The results suggested that transcription regulators, alternative splicing and the selective use of the transcription initiation site may control NURR1 expression and function (Torii et al., 1999). Furthermore, missense mutations in exon 3 of NURR1 have been linked to schizophrenia and manic-depressive disorder (Buervenich et al., 2000). Since the dysfunction of DAergic neurons is one of the major factors in PD, a preventive approach may be contrived by studying whether the disease is correlated with NURR1.
U.S. Pat. No. 6,284,539 describes methods to direct multipotential precursor cells from the central nervous system to adopt a dopaminergic cell fate. Generally, NURR1 is introduced into central nervous system (CNS) stem cells. In specific embodiments, in vitro neural populations enriched in dopaminergic cells for transplantation in Parkinson's Disease or other neurological disorders are generated. In other specific embodiments, there are methods for generating tyrosine hydroxylase expressing cells in a culture of mammalian CNS stem cells by culturing mammalian CNS stem cells in vitro, introducing a NURR1 polynucleotide that is expressed, incubating the mammalian CNS stem cells, and identifying tyrosine hydroxylase expressing cells in the culture.
U.S. Pat. No. 6,312,949 is related to a cell comprising an exogenous NURR1 nucleic acid that encodes an amino acid sequence that is expressed and induces tyrosine hydroxylase expression within the cell. In specific embodiments, the cells can be used to treat catecholamine-related deficiencies associated with disease states such as Parkinson's disease.
U.S. Pat. No. 6,395,546 is directed to methods for generating dopaminergic neurons in vitro from embryonic and adult central nervous system cells. Specifically, these cells are isolated, cultured in vitro and stimulated to differentiate into dopaminergic neurons by down-regulating COUP-TFI and/or COUP-TFII expression or increasing NOT1 expression.
Zetterstrom et al. (1996) describe in situ hybridization of NURR1 mRNA in the developing and adult mouse and rat in several regions during early central nervous system (CNS) development, suggesting it is involved in the development and maturation of specific sets of CNS neurons.
Finally, Buervenich et al. (2000) describe that direct sequencing of genomic DNA revealed two different missense mutations in the third exon of NURR1 in two schizophrenic patients and another missense mutation in the same exon in an individual with manic-depressive disorder. All three mutations caused a similar reduction of in vitro transcriptional activity of NURR1 dimers of about 30–40%. Neither of these amino acid changes, nor any sequence changes whatsoever, were found in patients with Parkinson's disease or control DNA material of normal populations.
Thus, there remains an absence in the art for association between NURR1 mutations and the etiology of Parkinson's disease.